1. Field of the Invention
The present invention relates to biological treatment of contaminated liquids and effluent, and, more particularly, to methods and apparatus for the creation and/or application of customized biology populations to biological processes, such as wastewater treatment.
2. Description of the Related Art
Before being discharged to the environment, contaminated waters from municipal, commercial, and industrial sources frequently must be treated to prevent harmful impacts. The treatment processes used are numerous and varied. A rudimentary conventional process is shown in FIG. 1. The treatment process often begins with a coarse removal step 110, in which the waste influent is typically treated by screening and grit removal processes. In some treatment processes, the coarse removal step 110 is followed by a surge tank or lagoon, sometimes known as an equalization tank or a flow equalization vessel (not shown), to provide hydraulic inventory and reduce flow surges through the treatment process. The coarse removal step 110 can be then followed by the removal of sludge and solids in a primary clarifier 112. Frequently the sludge from the primary clarifier 112 is partially consumed in a digester 114, which recycles clear effluent back to the start of the process and diverts the unconsumed sludge to disposal.
In some processes the clear effluent overflow from the primary clarifier 112 is stored in a flow equalization vessel (not shown). Such a vessel is used to provide inventory and to reduce flow surges through the treatment process. This clear effluent overflow from the clarifier may be mixed with activated sludge and aerated in an aeration unit 118 before being fed to a secondary clarifier 120 for secondary treatment. In some processes the aeration unit 118 has insufficient capacity to provide sufficient oxygen to meet the biological metabolism requirements of the microorganisms present in the waste stream. Such processes would benefit from additional oxygenation capacity.
The clear effluent overflowing the secondary clarifier 120 may be disinfected by a disinfecting unit 122, which may apply, for example, chlorine or UV light, and discharged to a local waterway as effluent. The solids from the secondary clarifier 120 are generally thickened, e.g., by a filter press 124 and then sent off for disposal.
Biological processes are commonly used for the elimination of contaminants in the secondary treatment portion of the process, and may take many forms. They generally involve exposure of the waste stream to one or more forms of microorganisms that stabilize or digest various contaminants. The microorganisms to be favored by the particular treatment process implemented are chosen to complement the waste stream in terms of content, strength, the biochemical and chemical environment used for treatment, and the specific effluent requirements. For example, the activated sludge process utilizes aerobic bacteria that remove the soluble biological oxygen demand (BOD) from wastewater. Practice of this process generally involves conducting wastewater into an aeration basin containing a suspension of digestive microorganisms, thereby forming a “mixed liquor” that is aerated to furnish oxygen for consumption of the BOD, the formation of new biomass, and the respiration of biomass maintained in inventory; the biomass sorbs, assimilates and metabolizes the BOD of the wastewater. After a suitable period of aeration, the mixed liquor is introduced into the secondary clarifier, in which the biomass settles, allowing the treated wastewater to overflow into an outlet effluent stream. All or a portion of the biomass separated from the effluent in 120 is returned to 118 to treat additional influent.
The BOD provided by the waste acts as “food” for the microorganisms. The BOD may be measured and reported as total BOD that includes both nitrogenous (NBOD) and carbonaceous oxygen demand (cBOD) or separately as NBOD and cBOD. This BOD, especially the cBOD, may be present in particulate or soluble form. The propensity of a given organism to metabolize a particular form of NBOD or cBOD and the rate at which this is done are determined by both the local environmental conditions and the number of organisms of similar type. In addition to carbonaceous “food,” microorganisms require certain macronutrients for survival, such as sodium, calcium, phosphorus, and/or nitrogen, and trace levels of micronutrients such as iron, sulfur, and/or manganese.
Controlled and efficient inclusion and removal of these macro and micronutrients with the waste stream are managed within the treatment process, and may be an important component of its operation with respect to meeting local effluent disposal requirements. Indeed, nutrients required for efficient operation of the treatment process may also contribute to environmental discharge concerns. For example, although certain microorganisms require phosphorus to survive, an excess of phosphorus in the treated waste stream can mandate addition of chemicals to precipitate and then coagulate and flocculate these materials to promote their separation and settling from the effluent to be discharged, whereupon the resulting sludge is commonly disposed of in a landfill.
As these various materials are metabolized by the microorganisms they may reproduce, and the degradable portions of the influent are converted into gases and excess biology. The excess biology may consist of live and/or expired microorganisms and other organic materials, and will generally be disposed of as sludge at the terminal portion of the process. The clear effluent that remains is generally discharged to a local receiving water body.
The microorganisms selected for the elimination of the contaminants in the incoming waste stream may come from many sources. Most waste treatment processes treat their incoming waste with recycled biology populations obtained from a downstream portion of the process. Recycling of these microorganisms is convenient and inexpensive, but unfortunately does not readily lend itself to the customized matching or tailoring of a given biological population to the varying needs of the influent waste stream. The composition, effectiveness, and amounts of the various recycled populations of microorganisms are also affected by the feed composition present when they were generated, so they are especially impacted by changes in the flow compositions or influent concentrations. These problems are exacerbated by the limited amount of flexibility most treatment plants have in manipulating the factors that favor a desired biological population profile. The options frequently are limited to the wasting of a portion of the sludge or some of its associated water chemistry, in an attempt to drive the biological selection process to a particular population balance by controlling the average “age” of the population, balancing the slower growing, more efficient organisms with the faster growing, more responsive organisms.
Partially in response to this need for varied populations, in response to local effluent requirements, and in an effort to accelerate the treatment process, a waste treatment plant may treat the waste stream with a combination of biological environments generally within the secondary treatment portion of the process. While virtually all treatment schemes utilize several major classes of bacteria, including obligate aerobes, facultative aerobes, nitrifiers, obligate anaerobes, and facultative anaerobes, manipulation of the different environments within the particular scheme favor different classes of bacteria that compete with each other in the course of the treatment process. The results of this competition affect the efficiency of the treatment process and the degree of treatment achieved in the final effluent.
Common to all of these processes, however, is generation of a waste stream of excess biology, generated because new growth exceeds death and decay. In most instances that waste stream also will contain particulate, seemingly non-degradable organic and inorganic material, in addition to the excess biology. Usually, the waste stream is removed as a portion of a solids recycle stream and it is directed to a terminal solids treatment process, thus minimizing the volume of excess waste solids that must be disposed of. The terminal treatment process functions primarily to concentrate and stabilize these materials for disposal and may include further biological treatment (“digestion”) that specifically enhances general death and decay of biomass.
Both as described and as generally practiced, the current waste treatment processes exhibit significant limitations. Conventional modes of operation do not allow microorganism populations to be tailored to the characteristics of a particular waste stream, which may change over time. Moreover, increasing the rate and extent of such biological processes would be desirable. Although minimizing the quantity of disposable solids is important to the performance of waste treatment systems, the ability to achieve low solids levels is impeded by the problems of excess biology and limited digestion, resulting in excessive operating costs, disposal costs, and potentially adverse environmental impacts.